Molecular Evolution of a Group of Microtubule-Associated Proteins Sharing Partial Similarities in Their Primary StructuresMolecular Evolution of a Group of Microtubule-Associated Proteins Sharing Partial Similarities in Their Primary StructuresAA12068302

Several microtubule-associated proteins (MAPs), including mammalian MAP2, MAP4, and τ, share a repeated motif called the assembly-promoting (AP) sequence, and the evolutionary relationship among the MAPs is claiming increased attention. In this report, we first searched the protein database for AP sequence-bearing proteins using the MAP4 repeat sequences as a query, and found some 600 proteins from 170 different species. We assessed the authenticity of the detected sequences by manually aligning them along the consensus sequence, v-sk-gs-nikh-pggg. Interestingly, the AP sequence-bearing proteins were found only in Bilateria, despite the importance of microtubules for all eukaryotes. The differentiation of the AP sequence-dependent microtubule regulation likely followed the emergence of Bilateria in biological evolution. Secondly, we closely inspected the resemblance of the AP sequences in the MAPs from three mammals and one nematode. By carefully comparing the AP sequences of the four MAPs, we discovered that the nematode MAP, PTL-1, is most similar to MAP4 among the three, although it was originally identified as a τ-like protein. From an evolutionary point of view, the closer relationship of PTL-1 to the ubiquitous MAP4 is more reasonable than to a protein restricted to mammalian brains.Full-length Paper